Transponder device

ABSTRACT

A transponder device receives a carrier signal from an interrogator unit. This carrier signal, of frequency F, is rectified by a rectifying circuit in order to generate operating power. Logic/timing circuits derive a clock signal and second carrier signal of frequency F/n from the received carrier signal. This clock signal reads a unique identifying data word from a programmable read only memory (PROM). The data word is encoded and mixed with the carrier signal in a balanced modulator circuit. The output of the balanced modulator is transmitted to the interrogator unit, where it is decoded and used as an identifying signal. The identifying signal identifies the particular transponder device from which it originated. The rectifier and balanced modulator circuits are realized from the same diode elements. All electrical circuits of the transponder device are realized on the same monolithic semiconductor chip. In one embodiment, and antenna receiving/transmitting coil is also part of the chip, being placed around the periphery thereof. In alternative embodiments, various hybrid elements may be connected to the monolithic elements in order to realize additional functions, such as adjustable tuning of the receiving circuit, independent crystal frequency control, and battery-powered operation.

This invention relates to electronic identification devices and systems,and more particularly to an electronic identification transponder devicethat is realized with miniaturized circuits built or fabricated on asingle monolithic semiconductor chip. This invention also relates to themanner of processing signals within such a transponder device.

BACKGROUND OF THE INVENTION

Electronic identification systems known in the art are generally one oftwo types: (1) tuned/detuned systems; and (2) transponder systems.

Tuned/Detuned Identification System

Tuned/detuned systems use tuned circuits that are selectively detuned byan identification element. (Alternatively, detuned circuits mayselectively be tuned by the identification element.) Such systems use acontroller/interrogator that sets up some form of magnetic field. Thisfield, when in close proximity to an identification element interactswith the identification element in such a way that the identificationelement can be identified. For example, in the absence of theidentification element, the electromagnetic field created by theinterrogator/controller exists in a tuned condition or state. However,as soon as the identification element is brought into close proximity tothe field, it interacts with the field in a way to detune it. The mannerand degree of detuning can then be measured and used to identify theparticular identification element employed. By affixing uniqueidentification elements (those which will interact with the field in aunique way) to a plurality of objects to be identified, such objects canbe electronically identified whenever they are brought within the fieldof the controller/interrogator by simply monitoring the manner anddegree of detuning that results. Advantageously, such identificationelements may be totally passive, requiring no external or internal powerfor operation. Thus, they can be realized in a relatively small space.As such, they are especially well suited for use in small, lightweight,inexpensive identification tags that can be placed on the objects to beidentified. U.S. Pat. Nos. 3,465,724 and 3,516,575 are examples of sucha tuned/detuned electronic identification system.

It is significant to note that the identification element used in suchtuned/detuned identification systems does not receive, process,generate, nor transmit any electronic signals. Rather, theidentification element merely interacts with the magnetic field createdby the interrogator/controller. This interaction can be thought of as aform of magnetic modulation that allows an identification to be madeonce the field is demodulated.

Because the identification element only interacts with the magneticfield created by the controller/interrogator, and is not required toreceive and process any electronic signals transmitted by theinterrogator/controller, and is not required to generate and transmitany responsive signals back to the interrogator/controller, theidentification element of a tuned/detuned identification system may berealized very inexpensively and compactly. Unfortunately, however,because there are only a limited number of ways that the magnetic fieldfrom the interrogator/controller can be modified or modulated, andbecause the identification element must typically be in very closeproximity to the interrogator/controller in order to measurably interactwith the magnetic field, such tuned/detuned identification systems arelimited in their use. Such systems will typically only be used inapplications involving a relatively small number of elements or types ofelements that are to be identified. Further, the elements to beidentified must be movable to the extent that they can be brought inclose proximity to the interrogator/controller.

Transponder Type Identification Systems

A second type of electronic identification system known in the art isthe transponder or transceiver system. Such systems employ a transponderor transceiver identification element that is affixed to the objects tobe identified. (It is noted that "objects", for purposes of thisapplication and as used hereinafter when referring to items, things,persons, or animals being identified by an identification element of theprior art or the present invention, refers to any thing or item thatneeds identifying, and includes stationary, movable, inanimate, oranimate objects). This transponder or transceiver element receives aninterrogation signal transmitted from a controller/interrogator unit.For purposes of this application, a transponder or transceiver elementis any device that receives an incoming interrogation signal andresponds thereto by generating and transmitting an outgoing responsivesignal. The outgoing responsive signal, in turn, is modulated orotherwise encoded so as to uniquely identify or label the particularobject to which the transponder element is affixed.

Because the amount of information that may be contained in the outgoingresponsive signal is typically limited only by the type of encodingused, and because modern encoding techniques allow a large amount ofinformation to be included therein, such transponder or transceiverelectronic identification systems are especially useful where arelatively large number of objects or types of objects need to beidentified. Applicant's U.S. Pat. No. 4,475,481 is an example of such atransponder/transceiver electronic identification system.

Further, because the incoming interrogation signal and the outgoingresponsive signal are typically RF signals that have been transmittedfrom an appropriate RF transmitter circuit, and because such signals cangenerally be transmitted over further distances than the interactivemagnetic field distances associated with detuned/tuned systems, thetransponder type identification system is more adaptable to applicationswhere the objects to be identified and the controller/interrogator unitare not necessary in close proximity to each other. (In thisapplication, the term "transponder" will hereinafter be used to meaneither "transponder" or "transceiver".)

Unfortunately, because RF transmitter and receiver circuits, as well asencoding and modulation circuits, must be employed within theidentification element of a transponder type system, such elements musteither carry their own independent power source (e.g., a battery) ormust include additional circuitry that allows the needed operating powerto be derived from the incoming RF signal. These additional power andcircuit requirements have not heretofore allowed the transponderidentification element of a transponder type identification system to berealized as inexpensively and compactly as would be desired for manyidentification applications.

What is needed, therefore, is a transponder type identification elementthat can be realized inexpensively and compactly in a very small space,thereby providing a transponder type identification system that includesall the advantages of similar prior art transponder type systems, butwhich eliminates the disadvantages thereof. The present inventionaddresses this and other needs.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a very small,inexpensive, reliable transponder device may be realized on a singlemonolithic semiconductor chip. This chip, in turn, may be incorporatedinto a very small lightweight tag or label that can be readily andunobtrusively affixed to or carried by movable or ambulatory objectsthat are to be identified. Such tags or labels may thus function as theidentification element of a transponder type identification system asdescribed above.

Advantageously, because the transponder device of the present inventionmay be realized on a single semiconductor chip, the entire transponderidentification element may be packaged in a housing that is much smallerthan any similar elements heretofore available. This much smaller sizeopens the door to electronic identification applications not previouslypossible. For example, in accordance with one embodiment of theinvention, the entire transponder device, including its receiving andtransmitting antenna coil and power circuits, may be realized on asingle semiconductor chip. The small size of a semiconductor chip allowsit to be affixed to very small articles, such as vials in a chemical orpharmaceutical processing plant, the location, batch, date code, etc.,of any individual vial of which can thereafter be electronicallymonitored.

The transponder device of the present invention includes receiving meansfor receiving a carrier signal from a controller/interrogator signal;and diode means for: (1) rectifying the received carrier signal in orderto generate the operating power for the device, and (2) mixing anencoded data word (used to identify the particular transponder devicebeing interrogated) with the carrier signal. Also included within thecircuits of the transponder device are data generating means forderiving a clock signal that is used to extract a unique code wordpreviously stored in a memory element of the device. This unique codeword is thereafter appropriately encoded in order to generate theencoded data word that is mixed with the carrier element. The mixing ofthe carrier signal with the encoded data word creates sum and differencesignals that are transmitted through appropriate transmitting means backto the controller/interrogator unit. Either the sum or difference signalthus serves as the responsive signal that is used to uniquely identifythe particular transponder device being interrogated.

An important feature of the present invention is the use of diodes tofunction both as a rectifier circuit and as a balanced modulatorcircuit.

Another important feature of the invention is the ability to generate aclock signal and data word from the incoming carrier signal, therebyobviating the need for additional, bulky, power-consuming oscillatorcircuits and modulation/demodulation circuits. Frequency stability ismaintained by using a crystal oscillator in the controller/interrogatorunit to generate the carrier signal. This carrier signal, when receivedat the transponder device, is then divided by an appropriate integer inorder to generate a stable and second carrier clock signal from whichthe identifying data word may be generated.

Still another important feature of the invention is the ability torealize all of the transponder circuits on a single monolithicsemiconductor chip. In one embodiment, even the receiving/transmittingantenna coil is placed around the periphery of the chip, therebyproviding a complete, self-contained, single chip transponder device.

The above and other features combine to provide a transponder devicethat is vastly improved over any prior art devices. For example, becausethe circuits can be realized on a single semiconductor chip, thetransponder function can be realized for a significantly lower cost.Further, because only a single chip is involved, fewer components areneeded to complete the identification system assembly, again resultingin reduced cost and significantly enhancing the system's reliability.

Alternative embodiments of the invention contemplate the use of varioushybrid elements to complement and enhance the circuits of the singlemonolithic semiconductor chip. For example, the addition of a hybridcapacitor and/or resistor allows selective tuning of the device's frontend circuits to the particular data rate that is employed. Further, theaddition of a hybrid crystal and associated elements allows the deviceto generate its own stable carrier frequency independent of the carrierfrequency from which operating power is derived. Also, the addition of ahybrid battery allows the device to be converted into a self-poweredbeacon device that periodically transmits its identifying encoded dataword without the need for the presence of a carrier signal. Forapplications where longer distance is required, the coil may be separatefrom the chip and larger than the chip in order to gather more signalstrength (power) from the controller/interrogator.

An electronic identification system is realized according to theteachings of the present invention through the use of acontroller/interrogator unit and a transponder device carried by eachobject to be identified. The controller/interrogator unit includes meansfor generating and transmitting a stable RF carrier signal. Thecontroller/interrogator unit also includes means for receiving aresponsive signal back from an interrogated transponder unit. Thetransponder unit includes the elements above described that permit it togenerate the responsive signal in response to receiving the RF carriersignal, i.e., means for receiving the carrier signal, diode means forrectifying the carrier signal in order to generate operating power forthe transponder unit and for mixing the carrier signal with an encodeddata word in order to generate the responsive signal, clock means forgenerating a clock signal that is derived from the carrier signal, datagenerating means for generating the encoded data word in synchrony withthe clock signal, and means for transmitting the responsive signal backto the controller/interrogator unit.

Further, in accordance with the teachings of the present invention, amethod is provided for processing a received power carrier signal in atransponder device used in an identification system. This methodincludes the steps of: (a) receiving the carrier signal, (b) rectifyingthe carrier signal in order to generate operating power for thetransponder device, (c) processing the carrier signal in order toproduce a clock signal and second carrier signal, (d) generating aunique data word signal using the clock signal, (e) mixing the secondcarrier signal with the power carrier signal in a balanced modulatorcircuit in order to generate sum and difference signals, the balancedmodulator circuit being realized from the same components as are used torectify the incoming carrier signal, and (f) transmitting the sum anddifference signals. In the preferred manner of practicing this method,the clock signal is derived from the carrier signal by simply dividingthe received carrier signal by an appropriate integer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention, as well asother features and advantages, will be more apparent from the followingmore particular description thereof presented in conjunction with thefollowing drawings, wherein:

FIG. 1 is a block diagram of an identification system, and illustratesthe interaction between a controller/interrogator unit and a transponderdevice;

FIG. 2 is a block diagram of the transponder device of FIG. 1;

FIG. 3 is a block diagram of the controller/interrogator unit of FIG. 1:

FIG. 4 is a schematic diagram of the circuits of the transponder deviceof FIG. 1;

FIG. 5 is a schematic diagram of the front end of the transponder deviceof FIG. 1, and illustrates the diode bridge circuit that functions bothas a rectifier circuit and a balanced modulator circuit;

FIG. 5A illustrates some of the signal waveforms associated with theoperation of the circuit of FIG. 5;

FIG. 6 is a schematic diagram of the front end of the transponder deviceof FIG. 1, and illustrates the use of additional hybrid components thatcan be connected to the transponder device in order to provide selectivetuning of the carrier receiving circuits;

FIG. 7 is a schematic diagram of the front end of the transponder deviceof FIG. 1, and illustrates the use of a hybrid crystal and batteryconnected thereto in order to provide additional flexibility in itsoperation;

FIG. 8 is a schematic diagram of the front end of the transponder deviceof FIG. 1, and illustrates the use of still additional hybrid elementsconnected thereto in order to provide selective gating off of a coilmodulator with a crystal oscillator; and

FIG. 9 is a top view of a monolithic semiconductor chip showing ageneralized topographical layout of the various types of circuits usedwithin the transponder device.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best presently contemplated mode ofcarrying out the invention. This description is not to be taken in alimiting sense but is made for the purpose of describing the generalprinciples of the invention. The scope of the invention should bedetermined with reference to the appended claims.

Referring to FIG. 1 there is shown a simplified block diagram of anidentification system. The system includes a controller/interrogatorunit 12 and a plurality of transponder devices or units 14, only one ofwhich is shown in FIG. 1. Each object to be identified carries atransponder unit 14. The controller/interrogator unit 12 transmits aninterrogation signal 16 that is received by the transponder unit 14.After receiving and processing the interrogation signal 16, thetransponder unit 14 transmits a response signal 18 back to thecontroller/interrogator 12. This response signal 18 has encoded thereinan identifying data word that is unique to the particular transponderunit 14 from which it originated. Hence, by positioning or placing thetransponder units 14 on the objects to be identified, it is possible toelectronically identify the people, animals, or other objects beingidentified.

Referring next to FIG. 2, a block diagram of the transponder unit 14 isshown. The interrogation signal 16 is received by an antenna coil 20. Inthe preferred embodiment, this interrogation signal is simply an RFcarrier signal that is applied to rectifier/balanced modulator circuit22 and divide/timing logic circuit 24 over signal line 26. Divide/timinglogic circuit 24 divides the carrier signal by an appropriate integer nin order to generate a clock signal and second carrier signal, on outputsignal line 28, having a frequency that is 1/nth of the frequency of theincoming carrier signal. The clock signal drives data generator circuit30, which circuit generates an encoded data word. This encoded data wordis presented over signal line 32 to the rectifier/balanced modulator 22.Also presented to the rectifier/balanced modulator 22, over signal line34, is a buffered carrier signal. This buffered carrier signal can beeither a "squared -up" version of the incoming carrier signal 16, or amodified carrier signal that has a frequency 1/2 or 1/4 of the incomingcarrier signal 16. The modified or buffered carrier signal and theencoded data word are mixed in the rectifier/balanced modulator 22 inorder to produce sum and difference signals. These signals appear onsignal line 26 and are presented to antenna coil 20, from which they aretransmitted as the responsive signal 18.

The incoming carrier signal 16 is also rectified by therectifier/balanced modulator circuit 22 in order to generate theoperating power used by the divide/timing logic 24 and the datagenerator 30. This operating power is distributed to these circuits overpower lines 36 and 38, respectively.

In FIG. 3, a block diagram of the controller/interrogator unit 1 isdepicted. While the present invention is primarily directed to thetransponder unit 14, and not to the controller/interrogator 12, somefeatures of the controller/interrogator 12 enhance the operation of thetransponder unit 14. For example, in the preferred embodiment, thecarrier or interrogation signal 16 is generated using a crystaloscillator 40 and appropriate transmission circuitry 42, includingtransmission antenna or coil 44. This action causes the carrier signal16 to have a very stable frequency. Because of this stable frequency, itis not necessary, in the preferred approach, to incorporate anothercrystal oscillator in the transponder unit 14.

The responsive signal 18 generated by the transponder unit 14 isreceived at the controller/interrogator 12 through antenna coil 46 andreceiver circuit 48. These components are tuned to the particularfrequency expected for this signal, which, as explained above inconjunction with FIG. 2, will be either the sum or difference frequencyresulting from mixing the encoded data word signal with the carriersignal. Further, a band pass filter circuit 50 (which may be includedwithin the receiver circuit 48) will further assure that only thosefrequencies of interest are passed on to the demodulation/decodecircuits 52. At the demodulation/decode circuits 52, the responsivesignal is demodulated and decoded using known demodulation and decodingtechniques in order to extract the data word signal included in theresponsive signal 18. This data word signal serves to identify theparticular transponder unit from which it originated. It can be storedin data log circuitry 54 and subsequently displayed by data displaycircuitry 56. Alternatively, concurrently with the storage of the dataword in data log circuitry 54, the data word may be displayed by datadisplay circuitry 56, or data may be sent to a central processor forfurther processing or control.

Hence, from the block diagrams of FIGS. 1-3, it is seen that inoperation the controller interrogator unit 12 generates and transmitsthe carrier (interrogation) signal 16. Upon receipt of this incomingcarrier signal 16, the transponder unit 14 generates a second carriersignal modulated by an encoded data word that is mixed with the carriersignal in rectifier/balanced modulator 22. This action produces theresponsive signal 18 that is transmitted back to thecontroller/interrogator 12, which responsive signal 18 uniquelyidentifies the transponder unit 14 from which it originated.

A schematic diagram showing all usable signals brought out to the pinsof transponder unit 14 is illustrated in FIG. 4. This diagram depictsall of the circuits that are included on the single monolithicsemiconductor chip, and further shows the nine pins of terminals,labeled 1-9, that are used to interface with these circuits. While theantenna coil 20 is not included in the diagram of FIG. 4, it is notedthat it too can be included on the semiconductor chip as shown in FIG. 9

Still referring to FIG. 4, it is seen that the circuitry is relativelysimple and that not a lot of circuit elements are required. Thissimplicity, unavailable heretofore in similar transponder devices, makespossible the incorporation of the device as a self-contained unit on asingle chip.

Referring next to FIG. 5, the front end of the circuits of FIG.4--principally the rectifier/balanced modulator circuits 22--will beexplained. From FIG. 5 it is seen that the rectifier/balanced modulator22 is realized with a diode bridge comprising diodes 60, 61, 62, and 63.The input terminals to this bridge circuit are pins 3 and 6. Anadditional diode 65 is inserted between and in series with diodes 61 and63. This diode 65 allows the modulated signal, when applied to therectifier/balanced modulator 22, to swing more and thereby increase thepercentage of modulation. Further resistors R1 and R2 are inserted intothe legs of the bridge circuit as shown in order to distribute thecurrent flow in an appropriate manner. In this regard, resistor R3 alsoserves to proportion the amount of signal current delivered to thedivide/timing logic 24 through pin 3. In the preferred configuration, R1has a value that is about 1/10th the value of R2, and R2 has a valuethat is about 1/10th the value of R3. Hence, in operation, most of thesignal current delivered through pin 3, e.g., during a positive halfcycle of the carrier signal, passes to the divide/timing logic 24 andnot to the bridge circuit portion that includes diode 62. However, whenpin 6 is positive with respect to pin 3, e.g., during a negative halfcycle of the carrier cycle, then most of the signal current passesthrough diodes 65 and 63 in order to charge the supply voltage.

A zener diode 66 is incorporated into the bridge circuit in order tostabilize the voltaqe VDD that is generated. In the preferredembodiment, the voltage VDD is around six volts, although any suitablevoltage level could be used. The bridge circuit uses the capacitanceinherent in all the circuit elements present on the chip to help storethe energy needed to maintain a sufficiently constant supply voltageVDD. This capacitance is shown in FIG. 4 as C1, but it is to beunderstood that C1 represents all of the distributed and other internalcapacitance present on the chip, and is not a separate element. In thisregard, the inventor has found that it is not necessary that the voltagesupply VDD be maintained at a constant level at all times. It issufficient, for the type of synchronous operation herein used, if thesupply voltage VDD is maintained at a prescribed level only when thecircuits are active (i.e., drawing current). For CMOS circuits, suchactivity only exists during a data transition. Because the operation ofthe device is essentially synchronous--everything occurs in synchronywith the clock signal, which in turn is in synchrony with the receivedcarrier signal--it is possible for the device to function so long as therequisite VDD voltage is present during the transitions of the carriersignal. Where the frequency of the carrier signal is sufficiently fast,as is the case here, the capacitance C1 doesn't have to hold a chargevery long in order for the device to operate. Hence, C1 (which, again,is comprised of all the distributed and internal capacitance on thechip) does not have to be very large in order for the device to operate.It is noted, for example, that the static current drain of a typicalCMOS chip is in the picoamp range.

Further, even when semiconductor devices other than CMOS circuits areemployed, such as TTL or GaAs devices, it is possible for the circuit tofunction during only a selected half cycle of the carrier signal bysetting up the logic circuits so that they only change states duringthis selected half cycle. Thus, it is possible to design the VDDgeneration circuitry so that it is primarily charging up during, forexample, the negative half cycle of the carrier signal, and design thelogic circuits so that they are not active until the positive half cycleof the carrier signal, at which time sufficient charge will be availableto provide the needed operating power.

FIG. 5A illustrates some of the foregoing principles of operationrelative to the circuit of FIGS. 4 and 5. In FIG. 5A, the incomingcarrier signal 16 from the controller/interrogator 12 is shown having afrequency Fo. After full-wave rectification, this signal substanitallyas a dc level having a ripple frequency of 2Fo. A second carrier signalis obtained by dividing the incoming carrier signal by two. This secondcarrier signal therefore has a frequency of Fo/2. This second carriersignal can, for desired embodiments, be used as a clock signal togenerate a data signal, two bits of which, "01", are shown in FIG. 5A.In turn, this data signal, gated with the second carrier signal Fo/2, isused to modulate the Fo carrier signal, realizing a modulated signal asshown at the bottom of FIG. 5A.

Also included as part of the rectifier/balanced modulator circuit 22 ofFIGS. 4 and 5 is NAND gate 68. This gate 68 serves to combine thecarrier signal (or a derivative of the the carrier signal), on signalline 34, with the encoded data, on signal line 32, and apply thiscombination to the diodes 60-63 of the bridge circuit. This actioncauses these signals to be mixed, resulting in sum and differencefrequencies that are presented to the output pins 3 and 6 (and hence tothe antenna coil 20) for transmission to the controller/interrogator 12or other receiving device.

It is noted that gate 68 of the rectifier/balanced modulator 22 also hasa control signal line 70 applied thereto, the function of which isexplained below in conjunction with the discussion of FIG. 8.

Referring next to the divide/timing logic portion 24 of FIG. 4, it isseen that the incoming carrier signal (received through pin 3) passesthrough resistor R3 and inverter gates 72 and 74. The output of gate 72is made available at pin 2, and the output of gate 74 is made availableat pin 1. These pins can be used as explained below in connection withthe discussion of FIGS. 6 and 7.

The output of gate 74 is presented to the clock input of a register 76.This register 76 divides the carrier signal by a appropriate factor.While the embodiment shown uses a simple series divide-by-2 arrangement,thereby providing outputs that have been divided by 2, 4, 8, 16, . . . ,the invention contemplates that other dividing schemes could be employedsuch that the carrier signal could be divided by any desired integer n.

The desired division of the carrier signal in register 76 provides aclock signal that has a frequency that is 1/nth of the carrierfrequency. Included in the divide/timing logic 24 are selection gates 78that allow the selection of different clock frequencies as controlled bya control signal applied to pin 9. The selected clock signal is thenpresented to the data generator circuitry 30 over signal line 28.

Data generator circuitry 30 includes a programmable read only memory(PROM) array 80 which is accessed through suitable memory control logicelements 82-85. Elements 82 and 84 are registers through which the clocksignal cycles. After a prescribed number of clock cycles, theseregisters address certain rows and columns of the memory array 80 inorder to extract the data that has been previously programmed therein.This data is passed serially to gate 86, as is the signal Q4 fromregister 84. As long as Q4 is high, the extracted data word is allowedto pass out of gate 86, over signal line 88, to Manchester encodercircuit 90. Manchester encoder circuit 90 encodes the data wordaccording to well known Manchester encoding techniques and presents theencoded data word to the rectifier/balanced modulator circuit 22 oversignal line 32. In the preferred embodiment, the encoded word is 64 bitslong, although any suitable bit length could be employed. Further,encoding schemes other than a Manchester encoding scheme could also beemployed.

The PROM memory array 80 may be realized using any suitable PROMconfiguration that can readily be incorporated on the same semiconductorchip as are the other transponder circuits. Preferably, an EEPROM(Erasable Electrically Programmable Read Only Memory) device could beused. Advantageously, during manufacture of the chip, or thereafter, thePROM can be easily programmed to contain an appropriate data word thatwould serve to uniquely identify that particular device. For example, amanufacturing date code in combination with a serial number could beemployed for this purpose. If the identifying data word programmed intothe device during manufacture did not suit the particular application,this data word could subsequently be erased using appropriate equipmentand a new, more suitable, data word could be programmed thereinto.

Also shown in FIG. 4 is a NAND gate 92 and an inverter gate 94. Theinverter gate 94 is connected to pin 9 and is used to condition acontrol signal applied to pin 9 as discussed below in conjunction withFIG. 8. The NAND gate 92 has one input connected to pin 7 and the otherinput connected to the data word signal output from the memory array 80through gate 86. The output of this NAND gate 92 is connected to pin 8.This gate 92 can be selectively connected to additional hybrid elementsas discussed below in connection with FIG. 8 in order to provideadditional options for using the transponder device.

Referring next to FIGS. 6-8, schematic diagrams of the front endcircuits of the transponder unit 14 are shown, as in FIG. 5, but furtherincluding additional hybrid elements connected thereto through the pinconnections provided. In FIG. 6, capacitor C2 is connected between pins1 and 3, and resistor R4 is connected between pins 2 and 3. Further,hybrid capacitors C3 and C4 are connected in tandem as shown betweenpins 4 and 5, and pins 5 and 6, respectively. Also, in FIG. 6, theantenna coil 20 is connected between ground, pin 5, and pin 6, in orderto disassociate it from interacting with R4 and C2. The values ofcapacitors C3 and C4 are selected as required in order to tune the frontend circuit to the particular carrier frequency that is employed. Thevalues of R4 and C2 are selected as needed in order to adjust the bittiming. Thus, flexibility is provided in order to make minoradjustments, i.e., tune the circuit, for the particular carrierfrequency that is used.

In FIG. 7, the single chip transponder unit 14 of the present inventionis converted to a more conventional transponder unit through the use ofa hybrid crystal oscillator circuit, comprising crystal Y1, capacitorC5, and resistor R5, and a battery B1. The crystal Y1 and resistor R5are connected across pins 2 and 3, while capacitor C5 is shunted frompin 3 to ground (pin 5). This configuration results in an oscillatorcircuit comprising the inverter gate 72, resistors R3 and R5, crystalY1, and capacitor C5. This oscillator circuit allows the data word to begenerated totally independent of the frequency of any incoming carriersignal. Further, when a battery B1 is employed, as shown, thetransponder device is no longer dependent on the carrier signal, andtherefore becomes a transmitting circuit that continually transmits itsidentifying signal. When a battery B1 is employed in this fashion, itwill typically have a voltage level output that is slightly less thanthat of zener diode 66, thereby keeping zener diode 66 turned off andeffectively out of the circuit.

In FIG. 8, a hybrid crystal Y2, capacitor C6 and resistor R6 areconnected as shown to pins 7 and 8 in order to create a crystaloscillator circuit that selectively transmits the data word through aseparate antenna 21. The crystal oscillator is realized withinternal-to-the-chip gate 92 and Y2, C6, and R6. Antenna coil 20 stillreceives a carrier signal and generates VDD therefrom. Further, thefrequency of the carrier signal determines the clock rate, which in turndetermines the rate at which the data word, appearing on signal line 88,appears. The crystal oscillator output signal, presented to antenna 21,is effectively modulated with the data word appearing on signal line 88.Because gate 92 is only active when VDD is present, the circuit of FIG.8 can thus function as a responding unit that transmits the data word ona carrier frequency independent of the incoming carrier signal. The useof a control signal applied to pin 9 further disables any signal frombeing mixed in the rectifier/balance modulator circuit 22, and hencefrom being transmitted through antenna 20, during the time that a signalis being transmitted from antenna 21. Such a control signal can simplybe realized by hardwiring pin 9 to desired potential.

It is noted that the circuits of FIGS. 6-8 represent only a portion ofthe various circuit configurations and options that could be realizedusing the single chip transponder device of the present invention.

FIG. 9 shows a topographical representation of the transponder chip 14in an embodiment that includes the antenna coil 20 as part of themonolithic chip. In accordance with this embodiment, the coil 20 isetched around the periphery of the chip substrate 98. In the center ofthe coil 20 are found a custom logic circuit 100, a programmable memoryarray 102, and memory control logic 104. Programmable memory array 102,which may be realized for example from an EEPROM deivce, comprises thememory array 80 depicted in FIG. 4. Memory control logic 104 comprisesthe memory control elements 82∝85 of FIG. 4, and the custom logiccircuit 100 includes the balance of the circuitry shown in FIG. 4. Thus,using the chip topography shown in FIG. 9, a functionally completetransponder unit 14 is realized on a single semiconductor chip.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the present invention. It is tobe understood therefore that within the scope of the appended claims,the invention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A transponder device comprising:receiving meansfor receiving a carrier signal from an external source; diode means forrectifying the received carrier signal in order to generate operatingpower for the transponder device, and for mixing an encoded data wordwith the carrier signal in order to generate sum and difference signals;digital circuit means for deriving a clock signal from said carriersignal; data generating means responsive to said clock signal forgenerating the encoded data word that is mixed with the carrier signalin said diode means; and transmitting means for transmitting the sum anddifference signals to a location external from said transponder device.2. The transponder device of claim 1 wherein said diode means comprisesa bridge circuit that functions both as a rectifer circuit and abalanced modulator circuit.
 3. The transponder device of claim 1 whereinsaid data generating means includes programmable read only memory (PROM)means, said PROM means having a unique code word previously programmedtherein from which said encoded data word is derived.
 4. The transponderdevice of claim 3 wherein said data generating means includes encodingmeans for encoding the unique code word programmed in said PROM means.5. The transponder device of claim 4 wherein said encoded data wordgenerated by the encoding means of said data generating means comprisesan n bit digital word, wherein n is an integer greater than
 7. 6. Anelectronic identification system for identifying a plurality of objectscomprising:a controller/interrogator unit for interrogating the objectsto be identified and processing the responses received, saidcontroller/interrogator unit including: means for generating an RFcarrier signal, said RF carrier signal comprising an interrogationsignal, means for transmitting said interrogation signal towards anobject to be identified, means for receiving a responsive signalgenerated in response to said interrogation signal, and means fordecoding, storing, and displaying the response received; and atransponder unit, carried by each object to be identified, comprising:receiving means for receiving the interrogation signal from saidcontroller/interrogator unit, diode means for rectifying the receivedinterrogation signal in order to generate operating power for thetransponder device, and for mixing an encoded data word with a digitalcarrier signal in order to generate sum and difference signals, said sumand difference signals comprising said responsive signal, digitalcircuit means for deriving a clock signal and said digital carriersignal from said interrogation signal, data generating means responsiveto said clock signal for generating the encoded data word that is mixedwith the digital carrier signal in said diode means, and transmittingmeans for transmitting the responsive signal to saidcontroller/interrogator unit.
 7. The identification system of claim 6wherein said RF generating means of said controller/interrogator unitincludes a crystal controlled oscillator, whereby the interrogationsignal, and all the signals derived therefrom, including the digitalcarrier signal and clock signal of said transponder unit, comprisefrequency stable frequency signals.
 8. A transponder device consistingof:receiving means for receiving a carrier signal from an externalsource; diode means for rectifying the received carrier signal in orderto generate operating power for the transponder device, and for mixingan encoded data word with the carrier signal in order to generate sumand difference signals; digital circuit means for deriving a clocksignal from said carrier signal; data generating means responsive tosaid clock signal for generating the encoded data word that is mixedwith the carrier signal in said diode means; and transmitting means fortransmitting the sum and difference signals to a location external fromsaid transponder device.
 9. In a transponder device, a method ofprooessing a received carrier signal and generating a response signalcomprising the steps of:(a) receiving the carrier signal through anantenna; (b) rectifying the carrier signal in order to generateoperating power for the transponder device; (c) processing the carriersignal in order to generate a clock signal; (d) generating a unique dataword signal using said clock signal; (e) mixing the data word signal andthe carrier signal in a balanced modulator circuit in order to generatesum and difference signals, said balanced modulator circuit comprisingthe same elements used to rectify the carrier signal in step (b); and(f) transmitting said sum and difference signals through said antenna.10. The method of claim 9 wherein step (c) of processing said carriersignal comprises dividing said carrier signal by an integer n, wherebysaid clock signal has a frequency that is 1/nth of the frequency of saidcarrier signal.